1. Field of the Disclosure
The present invention relates to downhole cleaning tools for use in oil and gas wells and in particular, though not exclusively, to a dual function cleaning tool adapted for cleaning a polished bore receptacle (PBR) and neighbouring casing on the same trip as setting a liner including the PBR.
2. Background Art
When a liner is cemented into casing located in a well bore, the PBR located at the top of the liner together with that part of the casing immediately above the PBR (herein referred to as the neighbouring casing) are susceptible to the influx of cement due to over displacement when the cement is pumped through the drill string and liner setting tool. Further when the drill string and setting tool are removed from the liner, cement and other debris located between the drill string and casing will fall back into the PBR and adhere to the neighbouring casing.
As the next stage requires the insertion of a sealing assembly into the liner, the PBR requires to have a smooth cylindrical inner bore on which an effective seal can be made. Additionally, the inner bore of the neighbouring casing is used to seal against a packer if a liner top packer is inserted, and thus requires to provide a smooth uniform cylindrical surface just above the PBR.
Consequently the presence of cement and debris at the PBR and/or the neighbouring casing provides a major problem in ensuring a successful seal. In order to overcome this problem, cleaning tools are typically run into the well bore to clean the PBR and the neighbouring casing. A trip is typically made to clean the PBR and a second trip is typically needed to clean the casing. Each trip into a well bore is both costly and time consuming.
Due to the decrease in inner bore diameter from the casing to the PBR, a single trip cannot be made into the well with a cleaning tool of a fixed diameter to clean both the PBR and casing. Cleaning tools with cleaning elements which are biased radially outwards such as that disclosed in U.S. Pat. No. 4,189,000 to Best, are inappropriate as the elements cannot be retracted at the point of entry to the PBR. Thus these tools can only clean the casing. Additionally as the cleaning elements are not located at the ends of the widest diameter of the tool, the cleaning elements cannot effectively access the neighbouring casing due to its close proximity to the narrower PBR.
It is therefore an object of the present invention to provide a cleaning tool which can provide the dual function of cleaning both the PBR and neighbouring casing on the same trip into a well bore.
It is a further object of at least one embodiment of the present invention to provide a cleaning tool which can provide the dual function of cleaning both the PBR and neighbouring casing on the same trip as the liner is set, and/or a packer is set.
It is a further object of at least one embodiment of the present invention to provide a cleaning tool which can effectively clean the inner bore of a PBR without damaging its relatively delicate inner surface while being able to effectively scrape the harder wearing inner surface of the neighbouring casing to effectively clean this also.
It is a yet further object of at least one embodiment of the present invention to provide a cleaning tool which can dress the top of the PBR while also cleaning both the PBR and the neighbouring casing on a single trip.
It is a yet further object of the present invention to provide a method of cementing a liner which includes the step of cleaning the PBR and neighbouring casing on tripping out the liner setting tool.